The adhesive made from film-forming materials that can be dispersed or dissolved in water is a water-based adhesive, also usually called an aqueous adhesive. With the film-forming materials generally being of organic polymers, gelatin, starch, dextrin, serum protein, albumin, methyl cellulose and polyvinyl alcohol all fall into this category of adhesives, together with soluble intermediates of some phenolic resins and urea-formaldehyde resins.
Not simply substituting water as a dispersion medium in the water-based adhesive for the solvent in the solvent-based adhesive, the water-based adhesive is different from the solvent-based adhesive mainly in the following aspects: The solvent-based adhesive, having a continuous phase, is a homogeneous system with organic solvents such as benzene and toluene as a dispersion medium, while the water-based adhesive is a heterogeneous system with water as the dispersion medium; the solvent-based adhesive has less molecular weight to keep coatability, while the viscosity of the water-based adhesive is independent of the molecular weight, not changing significantly with the molecular weight of the polymers, such that the molecular weight of the polymers can be greater to improve the cohesive strength of the adhesive.
Bonding strength is not only an important parameter of evaluating the quality of an adhesive, but also the almost only basis at present for judging whether a bonded joint is reliable. In order to quantitatively characterize strength of an adhesive, a specific method is needed to do a test on it. Among a lot of strength characterization methods, the lap shear test is applied most commonly: Applying the adhesive to one end of the material to be bonded, and overlaying the material with another material to be bonded in parallel to make the two materials bonded in parallel, with the bonding area being S; then doing a tensile test with a tensile tester to find out the maximum force Fmax at break. The lap shear strength (unit: Pa, generally kPa or MPa) can be calculated by dividing the maximum force Fmax by the bonding area S, i.e. Fmax/S, with the bonding strength of the adhesive measurable by comparing the lap shear strength. (A waja F.; Gilbert M.; Kelly G.; et al. Adhesion of polymers [j]. Prog Polym Sci. 2009, 34: 948)
The polymer composites are supramolecular aggregates formed based on intermolecular weak interactions such as electrostatic interaction, hydrogen bonds, coordination bonds, and host-guest interaction. The polymer composites mainly include polyelectrolyte-polyelectrolyte composites formed by polyanions and polycations, uncharged polymer-polymer composites, polymer-surfactant molecular composites, polymer-inorganic composites, and the like.
With the polymers being mixed under nonstoichiometric conditions, the formed composites are rich in remaining sites for interacting on the surface. Compared with the non-composite polymer, the polymer composite has a relatively large size and richer composition, and the structure of the polymer composite in the solution can be adjusted and controlled by changing the composite ratio of the polymer composite, temperature, pH of the solution, ionic strength, and other parameters.